A trundle bed is a type of bed that features a second mattress stored underneath the main bed. This design allows for easy storage and is ideal for small spaces, as it can be pulled out when needed and tucked away when not in use. Trundle beds are often used in children's rooms or guest rooms, providing an extra sleeping option without taking up much floor space. Typically, a trundle bed consists of a standard bed frame on top and a lower frame that can be wheeled out. The lower mattress is usually thinner than the upper one, making it easier to store. This versatile furniture piece is popular in homes where maximizing space is essential, such as in apartments or multi-purpose rooms.